River Valleys

Rationale: In the youthful stage of a river, vertical down-cutting is dominant over lateral erosion, resulting in deep, narrow valleys like gorges, canyons, and V-shaped valleys.

Rationale: W.M. Davis introduced the Geographical Cycle (Cycle of Erosion) in 1899, establishing the famous triad of structure, process, and time.

Rationale: Entrenched or incised meanders are deep cuts into the bedrock caused by renewed uplift or base level fall (rejuvenation), preserving the meandering pattern while deepening the valley.

Rationale: Playfair's Law states that every river has a valley proportioned to the size of the stream that flows through it, and junction angles are harmonious.

Rationale: Sea level is universally recognized as the ultimate base level of erosion below which a subaerial stream cannot erode its bed.

Rationale: A bajada is formed when adjacent alluvial fans merge along a mountain front to create a continuous depositional apron.

Rationale: Braided streams occur in environments with high sediment loads, highly variable discharges, and wide, shallow, easily eroded banks causing the channel to choke and split.

Rationale: A knickpoint represents an abrupt change in the slope of a river profile, frequently marking the boundary of rejuvenation or resistant rock strata.

Rationale: Monadnocks (residual hills) stand above the surrounding low-relief peneplain surface during the old stage of Davisian erosion.

Rationale: Dendritic drainage patterns develop on homogenous lithology and look tree-like with branching tributaries joining at acute angles.

Rationale: When headward erosion of an aggressive stream captures another stream, the bend where the diversion occurs is known as the elbow of capture.

Rationale: Horton demonstrated that stream numbers of successive orders form an inverse geometric series when plotted against stream order.

Rationale: Rivers carve V-shaped valleys through the combination of vertical stream down-cutting and mass wasting (slope collapse) of the valley walls.

Rationale: Alluvial terraces consist of remnants of former floodplains left standing above the new stream level due to channel incision into alluvium.

Rationale: J.T. Hack proposed the dynamic equilibrium theory, arguing that landforms adjust continuously to process rates in rocks of varying resistance rather than passing through sequential aging stages.

Rationale: Neck cut-offs during high floods straighten the channel, leaving the abandoned meander loop to form a crescent-shaped oxbow lake (billabong/dead lake).

Rationale: Potholes are circular or cylindrical hollows drilled into bedrock by turbulent swirling water carrying pebbles and sand grains (abrasion/corrasion).

Rationale: A graded stream achieves a delicate balance between transport capacity and sediment load, resulting in a smooth concave-upward longitudinal profile.